KNOW somethingto be something that you know and understand very well 是…非常熟悉的事物,是…很了解的事物
The natural world was an open book to him.
他对自然界了如指掌。
Examples from the Corpus
be an open book• I'd always thought of Jeff as an open book.• To them my futurewas an open book.• Our foreigndealingsare an open book generally a check book.